Copper and copper alloy components are commonly used in industrial systems due to copper's high thermal conductivity and anti-microbial properties. Copper and copper alloys (e.g., bronze and brass) are relatively resistant to corrosion as a result of protective film layers that naturally coat the surface of copper, which include an inner cuprous oxide film layer and an outer cupric oxide film layer. Under anaerobic conditions, these protective layers generally reduce the rate of further corrosion of the metal surface. However, under certain conditions, copper and copper alloys are susceptible to corrosion. In the presence of oxygen and under acidic conditions, oxidation of copper and dissolution of the copper (II) ion into water can occur.
Copper corrosion inhibitors are commonly added to industrial water systems to prevent and reduce dissolution of copper from system surfaces. In particular, the use of nitrogen-containing compounds such as azoles is well known for inhibiting the corrosion of copper and copper alloys. It is generally believed that the nitrogen lone pair electrons coordinate to the metal, resulting in the formation of a thin organic film layer that protects the copper surface from elements present in the aqueous system. Nitrogen-containing compounds such as azoles are also known to precipitate copper (II) from the aqueous solution, hindering corrosion that can occur due to galvanic reactions between copper and other metals.
Oxidizing halogens are commonly used as biocides in industrial systems to control slime and microbiological growth in water. The protective film provided by many azoles erodes in the presence of oxidizing halogens such as chlorine, hypochlorite, and hypobromite, reducing the effectiveness of the corrosion inhibitor. Moreover, a decrease in copper (II) precipitation often occurs in the presence of oxidizing halogens due to halogen attack of the corrosion inhibitor in solution. Thus, in the presence of oxidizing halogens, an excess or continuous injection of corrosion inhibitor is often required to maintain the organic protective film.
It would be desirable to provide a method of using a corrosion inhibitor that provides protection of copper in the absence and presence of oxidizing halogen agents.